Nonindigenous Aquatic and Semi-Aquatic Plants in Freshwater Systems

Nonindigenous Semi-Aquatic Plants

Catclaw Mimosa, Giant Sensitive Plant (Mimosa pellita) formally M. pigra.

The mimosa is indigenous to tropical Central and South America. It may have been introduced into North America as a botanical curiosity because its leaves fold on touch. There is some evidence that it was introduced into Florida as early as in 1926 (Fairchild 1944). Three small populations of this exotic plant species are in Florida now: near Sebring adjacent to the Loxahatchee River along the Martin-Palm Beach County borders and near the mouth of the St. Lucie River in Martin County. The infestation near the Loxahatchee River dates back to 1953 (Hall 1985). The extensive canals and wetlands of southern Florida are similar to habitats that have been invaded by catclaw mimosa elsewhere. It is an emersed plant along river banks, ditchbanks, and wetlands (Nall et al. 1986). Many scientists believe that this species rivals the ability of melaleuca to invade the Everglades wetland systems (Schardt and Schmitz 1990).

In Australia where the catclaw mimosa was introduced in the late 1800's (Miller and Lonsdale 1987), a largely intact natural swamp forest in a floodplain is now covered by dense monospecific stands of catclaw mimosa (Lonsdale et al. 1989). Braithwaite et al.(1989) reported that fewer birds and lizards, less herbaceous vegetation, and fewer tree seedlings were in catclaw mimosa stands than in surrounding native plant communities. Catclaw mimosa is an invasive plant and has recently been placed on the Federal Noxious Weed List (White 1984).

Eradication of catclaw mimosa in three sites was conducted by the Department of Natural Resources (Schardt and Schmitz 1990). Because single plants are sparsely dispersed among tall, native vegetation, selective eradication is difficult. Even seedlings resist hand pulling because the roots quickly anchor deeply into soils. Control has been attempted with only registered herbicides for use in aquatic sites because the sites are often wet. Eradication has been successful with foliar applications of glyphosate, 2,4-D or a combination of 2,4-D and dicamba. Regrowth from seeds is quick, and seeds seem to be viable for several years; therefore, treatments are routinely applied to control new growth and to prevent flowering and the formation of new seed beds (Schardt and Schmitz 1990).

In 1986, biologists of the Florida Department of Natural Resources collected seeds of Mimosa pigra from a wetland in Florida. Later, beetles emerged from these seeds and were identified as Acanthoscelides quadridentatus (Coleoptera: Bruchidae; Center and Kipker 1991). The previous range of this beetle was Texas, Mexico, Guatemala, Belize, Honduras, El Salvador, Nicaragua, Costa Rico, Panama, and South America (Johnson 1983). Some studies have been initiated to determine whether this beetle could be used as a biological control agent for the mimosa.